1. Field of the Invention
This invention relates to an expansion type mine roof bolt assembly and particularly to a chemical dispenser assembly that is added to the roof bolt to seal the base of the roof bolt hole in the roof strata from the adverse effects of moisture and oxygen in the air.
2. Description of the Prior Art
Mine roof bolts and rock bolts have been used in mines and tunnels to support roof and interior structures of mines and tunnels for a number of years. Roof bolts are used to strengthen the load bearing characteristics of roof and adjacent strata, particularly in stratified roof material. Certain types of mine roof strata, such as shale and clay type strata are vulnerable to degradation from the adverse reaction of said strata with moisture and oxygen present in the ambient mine air. Strata with only a small content of certain clays such as the montmorillonites and illites are very sensitive to contact with humid mine air. The moisture expands the clays causing a loss of cohesion in the strata. Pyrites and other minerals when present in the exposed roof strata react with the oxygen from the air and also react with both moisture and oxygen to change their chemical and physical form, destroying their binding and load bearing characteristics. When bolt holes are drilled in the mine roof strata the newly exposed strata is vulnerable to exposure to ambient mine air, also the newly exposed strata may expel innate gases and moisture trapped in the roof strata in its natural condition, such loss of gases and moisture also have a detrimental effect on the load bearing characteristics of the roof strata; also some of the gases are noxious and toxic and pose a safety hazard to mine operations.
By either coating the exposed bolt hole strata with a protective coating, or filling in the voids in the bolt hole with cementing or filler type material, the strata may be protected from the ambient mine air. A liquid or foam material such polyurethane may be used to coat the surfaces of the borehole or fill the voids in the borehole, or to seal the base of the borehole. The insertion of granular chemical substances such as desiccants (silica gel etc) and oxidants (iron filings etc) into the bore hole provide a means of counteracting the moisture and oxygen present in the mine air confined in the bore hole, if the base of the bore hole is sealed from the entrance of additional mine air. References to prior art is made to U.S. Pat. Nos. 25,869 and 2,829,502. Expansion type shell units are commonly used in roof control by mine roof bolt assemblies. The expansion shell type roof bolt assembly consists of a bolt up to several feet in length, a base plate with a hole in it through which the roof bolt is inserted, and an expansion shell unit which is threaded on the threaded upper end of the roof bolt stem. When the roof bolt assembly is inserted into the bore hole in the mine roof, the bolt is tightened, by rotation, causing the expansion shell to expand and anchor the bolt assembly in the bolt hole and binding the stratified roof material tightly together. The expansion shell usually consists of a threaded wedge nut, a cylindrical shell slotted to form wings that are semi-rigid, and a bail or hanger that serves both as a stabilizer to prevent rotation of the shell in the hole when it is first rotated, and the bail also holds the wings of the expansion wings of the shell in a fixed position with relation to the top of the bolt stem, so that as the wedge nut is rotated, the wedge advances downward on the treaded portion of the roof bolt stem which forces the expansion wings outward against the sides of the bolt hole causing the shell to anchor the assembly in place.
There are various types of chemical roof bolt assemblies which usually consist of a sealed pouch containing a chemical cement that sets when the pouch is ruptured and the chemicals mixed by rotation of the bolt stem within the bolt hole. The chemicals solidify filling the voids with the chemical cement.